The proliferation and increased usage of portable computer and electronic devices has greatly increased demand for memory cells. Digital cameras, digital audio players, personal digital assistants, and the like generally seek to employ large capacity memory cells (e.g., flash memory, smart media, compact flash, or the like). Memory cells can be typically employed in various types of storage devices. Storage devices include long term storage mediums such as, for example, hard disk drives, compact disk drives and corresponding media, digital video disk (DVD) drives, and the like. The long term storage mediums typically store larger amounts of information at a lower cost, but are slower than other types of storage devices. Storage devices also include memory devices which are often, but not always, short term storage mediums.
In addition, memory cells can generally be subdivided into volatile and non-volatile types. Volatile memory generally requires periodic refresh cycles in order to maintain information. Such memory cells include, for example, random access memory (RAM), dynamic RAM (DRAM), synchronous RAM (SRAM) and the like. Unlike volatile memory, non-volatile memory cells typically maintain information when power is removed. Examples of non-volatile memory cells include; read only memory (ROM), programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), flash memory, and the like. Volatile memory cells generally provide faster operation at a lower cost as compared to non-volatile memory cells. Nonetheless, to retain the information, the stored data typically must be refreshed.
Memory cells within a memory device can be accessed or “read” to retrieve stored information, “written” to store information, and “erased” to remove stored information. In general, memory cells maintain information in an “off” or an “on” state, also referred to as “0” and “1”. Typically, a memory device is addressed to retrieve a specified number of byte(s) (e.g., 8 memory cells per byte, 16 memory cells per word . . . ). As noted above, with volatile memory devices memory cells must be periodically “refreshed” in order to maintain state. Such memory devices usually are fabricated from semiconductor structures that perform various functions and that are capable of switching and maintaining the two states. Such devices are often fabricated with inorganic solid state technology, such as, crystalline silicon devices. A common semiconductor device employed in memory devices is the metal oxide semiconductor field effect transistor (MOSFET).
Increasing demand for information storage has lead memory device manufacturers to continuously research and develop technology that increases speed and storage retrieval of memory devices (e.g., increase write/read speed). At the same time, to reach high storage densities, manufacturers typically focus on scaling down semiconductor device dimensions (e.g., at sub-micron levels). Nonetheless, formation of various transistor type control devices that are typically required for programming memory cell arrays increase costs and reduces efficiency of circuit design. Therefore, there is a need to reduce structural complexities of conventional memory devices and simplify fabrication processes of memory devices. In addition, a typical fabrication process requires etching (e.g., of copper) and a deposition processes with good gap-fill capability for both dielectric and metal layers. Conventional metal etch and dielectric gap-fill techniques present challenges in the drive towards smaller semiconductor dimensions.